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## CHAPTER 3 Lists, Stacks, and Queues

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**CHAPTER 3**Lists, Stacks, and Queues §1 Abstract Data Type (ADT) 【Definition】Data Type = { Objects } { Operations } 〖Example〗 int = { 0, 1, 2, , INT_MAX, INT_MIN } { , , , , , } 【Definition】An Abstract Data Type (ADT) is a data type that is organized in such a way that the specification on the objects and specification of the operations on the objects areseparated fromthe representation of the objects and the implementation on the operations. 1/18**§2 The List ADT** ADT: Objects: ( item0, item1, , itemN1 ) Operations: Finding the length, N, of a list. Printing all the items in a list. Making an empty list. Finding the k-th item from a list, 0 k < N. Inserting a new item after the k-th item of a list, 0 k < N. Deleting an item from a list. Finding next of the current item from a list. Finding previous of the current item from a list. Why after? 2/18**§2 The List ADT**Address Content …… …… array+i itemi array+i+1 itemi+1 …… …… 1. Simple Array implementation of Lists array[ i ] = itemi Sequential mapping MaxSize has to be estimated. Find_Kth takes O(1) time. Insertion and Deletion not only take O(N) time, but also involve a lot of data movements which takes time. 3/18**§2 The List ADT**ptr ptr Address Data Pointer SUN QIAN ZHAO ZHAO QIAN LI 0010 0011 0110 1011 SUN QIAN ZHAO LI 1011 0010 0011 NULL Head pointer ptr = 0110 NULL 2. Linked Lists NULL To link ‘ZHAO’ and ‘QIAN’: list_ptr N1, N2 ; N1 = (list_ptr)malloc(sizeof(struct list_node)); N2 = (list_ptr)malloc(sizeof(struct list_node)); N1->data = ‘ZHAO’ ; N2->data = ‘QIAN’ ; N1->next = N2 ; N2->next = NULL ; ptr = N1 ; Locations of the nodes may change on different runs. Initialization: typedef struct list_node *list_ptr; typedef struct list_node { char data [ 4 ] ; list_ptr next ; } ; list_ptr ptr ; 4/18** takes O(1) time.**§2 The List ADT node ptr ... ... b ai+1 an a1 ai NULL temp Insertion temp->next = node->next node->next = temp Question: What will happen if the order of the two steps is reversed? Question: How can we insert a new first item? 5/18** takes O(1) time.**§2 The List ADT pre ptr ... ... an ai a1 b b ai+1 NULL node node Deletion pre->next = node->next free ( node ) Question: How can we delete the first node from a list? Answer: We can add a dummy head node to a list. Read programs in Figures 3.6-3.15 for detailed implementations of operations. 6/18**§2 The List ADT**llink rlink item item3 item2 item1 H H Doubly Linked Circular Lists typedef struct node *node_ptr ; typedef struct node { node_ptr llink; element item; node_ptr rlink; } ; Uhhh ... Then I’ll have to go from the 1st node again. But hey, why do I wantta find the previous node? Don’t we have enough headache already? Why do we need the doubly linked lists? ptr = ptr->llink->rlink = ptr->rlink->llink I’ll go from the 1st node to the m-th node. Suppose you have a list 1->2->3->…->m. Now how would you get the m-th node? Why do you ask me? :-) Maybe you wantta delete the m-th node? A doubly linked circular list with head node: Then you are asked to find its previous node m 1? An empty list : 7/18**§2 The List ADT**Two Applications The Polynomial ADT Objects : P ( x ) = a1 x e1 + + an x en ; a set of ordered pairs of < ei , ai > where ai is the coefficient and ei is the exponent. eiare nonnegative integers. Operations: Finding degree, max { ei}, of a polynomial. Addition of two polynomials. Subtraction between two polynomials. Multiplication of two polynomials. Differentiation of a polynomial. 8/18**§2 The List ADT**【Representation 1】 typedef struct { int CoeffArray [ MaxDegree + 1 ] ; int HighPower; } *Polynomial ; Try to apply MultPolynomial (p.53) On P1(x) = 10x1000+5x14+1 and P2(x) = 3x19902x1492+11x+5 -- now do you see my point? I like it! It’s easy to implement most of the operations, such as Add and Multiplication. Really? What is the time complexity for finding the product of two polynomials of degree N1 and N2? O( N1*N2 ) What’s wrong with that? 9/18**§2 The List ADT**Given: We represent each term as a node Coefficient Exponent Next …… a0 am1 e0 em1 NULL a 【Representation 2】 Home work: p.79 3.6 Add two polynomials Declaration: typedef struct poly_node *poly_ptr; struct poly_node { int Coefficient ; /* assume coefficients are integers */ int Exponent; poly_ptr Next ; } ; typedef poly_ptr a ; /* nodes sorted by exponent */ 10/18**§2 The List ADT** Multilists 〖Example〗 Suppose that we have 40,000 students and 2,500 courses. Print the students’ name list for each courses, and print the registered classes’ list for each student. 【Representation 1】 int Array[40000][2500]; 11/18**§2 The List ADT**S1 S2 S3 S4 S5 C1 C2 C3 C4 【Representation 2】 Home work: Self-study the sparse matrix representation on p.50 12/18**§2 The List ADT**… … 0 1 2 S-1 Cursor Space Element Next 1 2 3 S-1 0 3. Cursor Implementation of Linked Lists (no pointer) Features that a linked list must have: • The data are stored in a collection of structures. Each structure contains data and a pointer to the next structure. • A new structure can be obtained from the system’s global memory by a call to malloc and released by a call to free. Note: The interface for the cursor implementation (given in Figure 3.27 on p. 52) is identical to the pointer implementation (given in Figure 3.6 on p. 40). 13/18**§2 The List ADT**p p p … … … … 0 0 1 1 2 2 S-1 S-1 Element Next Element Next 2 2 5 5 S-2 S-2 0 0 x Home work: p.80 3.12 Reverse a singly linked list malloc: p = CursorSpace[ 0 ].Next ; CursorSpace[ 0 ].Next = CursorSpace[ p ].Next ; 2 free(p): CursorSpace[ p ].Next = CursorSpace[ 0 ].Next ; CursorSpace[ 0 ].Next = p ; Read operation implementations given in Figures 3.31-3.35 Note: The cursor implementation is usually significantly fasterbecause of the lack of memory management routines. 14/18**§3 The Stack ADT**5 6 1. ADT 6 A stack is a Last-In-First-Out (LIFO) list, that is, an ordered list in which insertions and deletions are made at the top only. 5 4 Objects: A finite ordered list with zero or more elements. 3 5 2 Operations: Int IsEmpty( Stack S ); Stack CreateStack( ); DisposeStack( Stack S ); MakeEmpty( Stack S ); Push( ElementType X, Stack S ); ElementType Top( Stack S ); Pop( Stack S ); 6 1 Note: A Pop(orTop) on an empty stack is an error in the stack ADT. Push on a full stack is an implementation error but not an ADT error. 15/18**§3 The Stack ADT**TmpCell FirstCell S S S Element Element Element Element NULL 2. Implementations Linked List Implementation (with a header node) TmpCell->Next = S->Next Push: S->Next = TmpCell Element Top: return S->Next->Element Pop: FirstCell = S->Next S->Next = S->Next->Next free ( FirstCell ) Easy! Simply keep another stack as a recycle bin. But, the calls to malloc and free are expensive. 16/18**§3 The Stack ADT**Array Implementation struct StackRecord { int Capacity ; /* size of stack */ int TopOfStack; /* the top pointer */ /* ++ for push, -- for pop, -1 for empty stack */ ElementType *Array; /* array for stack elements */ } ; Note: The stack model must be well encapsulated. That is, no part of your code, except for the stack routines, can attempt to access the Array or TopOfStack variable. Error check must be done before Push or Pop (Top). Read Figures 3.38-3.52 for detailed implementations of stack operations. 17/18**§3 The Stack ADT**Check if parenthesis ( ), brackets [ ], and braces { } are balanced. 3. Applications Balancing Symbols Algorithm { Make an empty stack S; while (read in a character c) { if (c is an opening symbol) Push(c, S); else if (c is a closing symbol) { if (S is empty) { ERROR; exit; } else { /* stack is okay */ if (Top(S) doesn’t match c) { ERROR, exit; } else Pop(S); } /* end else-stack is okay */ } /* end else-if-closing symbol */ } /* end while-loop */ if (S is not empty) ERROR; } T( N ) = O ( N ) where N is the length of the expression. This is an on-line algorithm. 18/18